Implantable medical devices may provide stimulation current to a stimulation site within a body of a patient to excite certain tissues to treat a medical condition. In some cases, the area to be stimulated may require a degree of precision such as where stimulating surrounding tissue is undesirable. Furthermore, due to physiological constraints on where electrodes can be positioned, the particular tissue to be stimulated may not be immediately adjacent the electrodes that provide the stimulation current.
Conventional current steering techniques include the transverse tripole, which is used for spinal cord stimulation. The transverse tripole uses two anodes and a central cathode place at the midline of the spinal column. Two simultaneous stimulation pulses of different amplitudes are provided via this tripole configuration, which has the effect of shielding lateral tissues from receiving stimulation and focusing the stimulation current relative to the midline.
While the transverse tripole configuration may provide a degree of stimulation current steering relative to the midline, the issues noted above are not addressed. Namely, the transverse tripole configuration does not push the stimulation current deeper into the tissue without a corresponding increase in stimulation current magnitude, where such an increase in magnitude creates increased stimulation also in the immediate vicinity of the electrodes. Thus, the transverse tripole configuration does not address situations where the tissue immediately adjacent the electrodes should not be stimulated.
Furthermore, such conventional efforts at current steering do not prevent the stimulation current from penetrating beyond the targeted tissue. Therefore, stray stimulation current may also provide unwanted stimulation to tissues beyond the targeted tissue.